What is the author's style in The Hollow Hills by Mary Stewart?

Merlin’s narrative language is fluid and smooth. However, he uses Roman and Old English names interchangeably. For instance, Magnus Maximus is the Roman name for Macsen Wledig. Most of the time, though, Merlin refers to people by their Old English names (Cei and Bedwyr are two examples; they are known to most modern-day English speakers as Kay and Bedivere). This is to show the significance of the time period; 5th century England saw a major change in its culture as the Britons shed their Roman ancestry and forged a new identity.